1. Field of the Invention
The present invention relates to polymerizable organic compositions and polymerizates obtained therefrom having a refractive index of at least 1.6, an Abbe number of at least 33 and an initial Barcol hardness of at least 1. More particularly, the present invention relates to certain polymerizable organic compositions comprising a radically polymerizable monomer having at least two (meth)acryloyl groups and backbone linkages selected from thiourethane linkages and/or dithiourethane linkages. The present invention also relates to photochromic articles prepared from such polymerizable compositions.
2. Description of the Prior Art
A number of organic polymeric materials, e.g., plastics, have been developed as alternatives and replacements for glass in applications such as optical lenses, fiber optics, windows and automotive, nautical and aviation transparencies. As used herein, the term ‘glass’ is meant to refer to silica-based inorganic glass. These polymeric materials can provide advantages relative to glass, including, shatter resistance, lighter weight for a given application, ease of molding and ease of dying. Representative examples of such polymeric materials include, poly(methyl methacrylate), thermoplastic polycarbonate and poly[diethylene glycol bis(allylcarbonate)].
The refractive indices of many polymeric materials are generally lower than that of glass. For example, the refractive index of poly[diethylene glycol bis(allylcarbonate)] is about 1.50, compared to that of high index glass, which can range, for example, from 1.60 to 1.80. When fabricating lenses to correct a given degree of visual defect, e.g., a correction for myopia, the use of a polymeric material having a lower refractive index will require a thicker lens relative to a material having a higher refractive index, e.g., high index glass. If the degree of correction required is substantial, as in the case of severe myopia, a lens fabricated from a low index polymeric material can be required to be very thick. A very thick lens may negate any benefit of reduction in weight relative to an equivalent degree of correction obtained from a higher refractive index lens, e.g., a high index glass lens. In addition, thicker optical lenses are not aesthetically desirable.
It is known that polymeric materials having refractive indices greater than 1.50 can be prepared from aromatic monomers and monomers containing halogens and/or sulfur atoms. The materials from which lenses, and in particular optical lenses, are fabricated can be categorized by their refractive indices. As is known to those of ordinary skill in the art, low indices typically include indices of refraction of from less than 1.50 through 1.53; middle indices comprise indices of refraction of from 1.54 through 1.57; and high indices commonly include indices of refraction of 1.58 and greater. Lenses prepared from polymeric materials having high refractive indices typically also have lower Abbe numbers (also known as nu-values). Lower Abbe numbers are indicative of an increasing level of chromatic dispersion, which is typically manifested as an optical distortion at or near the rim of the lens.
U.S. Pat. No. 5,384,379 to Bader et al. discloses sulfur-containing poly(meth)acrylates for optical applications. Although the materials disclosed by Bader et al. can be used as lenses to provide optical corrections, the poly(meth)acrylates disclosed generally provide an inadequate refractive index and chromatic dispersion. They also, generally, have poor impact resistance.
It is accordingly desirable then to identify new polymerizable organic compositions, which can be used to prepare transparent polymerizates, particularly optical lenses, that possess a combination of high refractive index and adequately high Abbe numbers. It is further desirable that these polymeric materials also possess physical properties, and in particular thermal properties, that are at least equivalent to and preferably better than those of lower index polymeric materials.